In paper making machines, suction rolls are commonly used to extract water from the wet paper web before it leaves the felt in the wet forming section of the paper making machine. The suction roll comprises a cylindrical metal shell in which a large number of small evenly spaced holes are formed. The suction roll typically rotates in contact with the felt at web speed and direction. Suction is applied to the inside surface of the roll by means of a suction box. The suction box is an elongated tube inside the suction roll and is fixed against rotation. The suction box has a longitudinal slot which is in sealing engagement with the inside surface of the suction roll. As the rotating inside surface of the suction roll passes over the slot, suction is applied through the holes to assist in de-watering the felt and thereby reduce the water content of the wet paper web.
Plugging of the suction roll holes is a commonly encountered problem. The "white water" extracted from the felt contains substantial insoluble components which tend to build up in the suction roll holes. Unless the suction roll is cleaned periodically, this build-up can lead to complete plugging of the suction roll. In such a case, the suction roll must be removed from the paper-making machine and the holes must be manually cleared. This is typically achieved either by manually punching out the obstruction on each hole with a hammer and punch. Given that there are hundreds of thousands of holes in a conventional suction roll, this operation is time consuming and the labour and down-time associated therewith is costly. In addition, such an operation carries with it the risk of damaging the suction roll.
There exist a number of known methods and apparatus which are intended to prevent the build-up of deposits during the paper-making operation and thereby avoid or make less frequent the requirement to manually clear the suction roll holes. For example, in U.S. Pat. No. 4,975,150 Yasuda et al. there is disclosed a method of preventing the plugging of a suction roll with makes use of the conventional fan sprays which are conventionally fitted inside the suction roll. These fan sprays apply a coating of white water to the inside surface of the suction roll to improve sealing and reduce friction between the suction box slot opening and the inside surface of the suction roll. While the pressure of the fan head spray is insufficient to dislodge deposits in the suction roll holes, Yasuda et al. disclose the use of maleic acid in the fan spray as an anti-plugging agent.
It is also known to provide a dedicated high pressure spray head to clean various perforated elements. For example, in U.S. Pat. No. 5,494,227 Costantini, there is disclosed a shower system having an arcuate array of high pressure spray nozzles mounted for lateral reciprocal movement across a screen which functions to separate pulp by size. Similarly, in U.S. Pat. No. 4,167,440 Falk there is disclosed a high pressure reciprocating spray cleaning apparatus for foraminous elements.
It is also known to provide cleaning fluid in a dedicated pressure chamber located inside the suction box for the purpose of cleaning felts. For example, in U.S. Pat. No. 1,840,102 Jespersen, there is disclosed a pressure chamber which extends across the width of the suction roll and applies water under pressure through the suction roll perforations to clean the felt. Similarly, in U.S. Pat. No. 3,190,793 Starke, there is disclosed a pressure chamber employing cleaning fluid subject to high frequency oscillations to clean paper making machine felts.
None of these known systems disclose any means to provide a high pressure cleaning fluid into a suction box for cleaning the perforations in a rotating suction roll.